Barycentric quad coordinates for the point on the mesh face mesh.Faces[FaceIndex]. If the face is a triangle disregard T[3] (it should be set to 0.0). If the face is a quad and is split between vertices 0 and 2, then T[3] will be 0.0 when point is on the triangle defined by vi[0], vi[1], vi[2], and T[1] will be 0.0 when point is on the triangle defined by vi[0], vi[2], vi[3]. If the face is a quad and is split between vertices 1 and 3, then T[2] will be 0.0 when point is on the triangle defined by vi[0], vi[1], vi[3], and m_t[0] will be 0.0 when point is on the triangle defined by vi[1], vi[2], vi[3].